Master program CORELIS 1 course student Kobzar G
*Stomata (Greek stoma-mouth) are intracellular fissures and specialized guard cells that are found on the epidermis of leaves, stems, ovules and some flowers. The stomata allow the exchange of carbon dioxide, oxygen and water vapor between the plant and the atmosphere. *Most stomata are between 20 to 80 µm in diameter. Plant epidermal tissue may contain 10, 000 to over 100, 000 stomata per cm². The density of stomata is related to the species of the plant, but can also vary due to the environmental conditions under which the plant is growing. Changes in atmospheric CO 2 concentrations have a particularly strong impact on stomata density. Increasing CO 2 leads to significant decreases in stomata densities in many plants. 2/10
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The two paleoenvironmental applications of stomata analysis are: *1) the reconstruction of past vegetation using the presence, absence and abundance of stomata microfossils of different plant taxa; *2) the reconstruction of changes in atmospheric CO 2 concentrations and the impact of such changes on plant physiology through examination of changes in the density of stomata on modern and fossil leaves. 4/10
*The usefulness of conifer stomata in paleoecology, particularly as an ancillary technique to pollen analysis, arises from five factors: *First, the stomata cells of conifers are lignified. These lignified cells are more resistant to decay when deposited in lake waters than are unlignified soft tissue. *Second, stomata are generally deposited in lakes on whole leaves and large leaf fragments. In this regard, their taphonomy is more similar to that of plant macrofossils than to the taphonomy of pollen. *Third, microfossil stomata found in lake sediments occur as detached individuals and on small fragments of epidermis. *Fourth, many conifer stomata can be identified to species or genus using transmitted light microscopy. *Fifth, individual stomata are roughly the same size as most pollen grains. The lignified stomata can withstand the chemical treatments used in pollen preparation 5/10
*Preparation of samples for stomata analysis is identical to the chemical digestion techniques used for pollen preparations. However, removal of large organic fragments using selective sieving is sometimes applied during pollen sample preparation, but can decrease stomata abundance in samples. *Identification and counting of fossil stomata is conducted using transmitted light microscopy at a magnification of 400×. The concentration of stomata is far less than the concentration of pollen and spores. Stomata are generally found at concentrations of < 2000 per ml. *The most appealing quality of fossil stomata analysis is its ability to provide a relatively precise indicator of the past local presence or absence of coniferous plants. The potential of fossil stomata to improve upon the spatial resolution provided by pollen analysis can be assessed by comparing the relationship between the pollen and stomata content of modern lake sediments and the modern distributions of conifers. 6/10
*Stomata and pollen records from lake sediment cores *Stomata records have been obtained from late Quaternary lake sediment cores taken in Europe, Siberia and North America. Stomata have also been recovered analyzed from peatlands. *In studies from the Alps, fossil stomata have been recovered along with pollen from a number of sites. The stomata of Picea abies (European spruce), Pinus and Larix decidua (European larch) have been used to reconstruct changes in the position of upper treeline. Stomata from Juniperus, Pinus and Abies alba (fir) have been used to reconstruct lower elevation vegetation change. Both natural vegetation change and anthropogenic changes have been detected using stomata analysis. In all cases, the abundance of stomata in the sediments is much less than that of the associated pollen. 7/10
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Summary * Microfossils of conifer stomata offer considerable benefits as a paleoecological tool. Conifer stomata are frequently present in the same silty organic lake sediments from which pollen and other microfossils are recovered. Unlike pollen, stomata are not prone to long distance transport and provide a good indication of the local presence or absence of plant taxa. In this regard, stomata are similar to plant macrofossils such as seeds and leaves. However, microfossil stomata are deposited throughout lakes in a manner similar to pollen. Thus, stomata may be more frequently obtained from lake sediment cores than is the case for plant macrofossils. Stomata are recovered during the normal processing of samples for pollen analysis and can be identified and counted at the same time as pollen. Stomate identification is relatively easy and the taxonomic resolution is usually as good, or better, than for pollen. * Analysis of microfossil stomata has been conducted on a mere handful of lake sediment cores compared with the many cores analyzed for fossil pollen. The ease of conducting conifer stomate analysis, and the benefits of the technique in terms of spatial resolution, will generate the increasing use of the technique on new sites. In addition, many samples that have been previously prepared analyzed for pollen likely contain conifer stomate records. It is likely that many of these older records could be easily reanalyzed to count stomata and provide additional information on past vegetation. 9/10
Thank you for attention! If you have any questions I'll be glad to answer by email: kobzargv@mail. ru
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